1. Field of the Invention
The present invention pertains to a sliding constant-velocity joint, particularly for longitudinal drives of motor vehicles.
2. Description of the Prior Art
Generally, the shafts of longitudinal drives for motor vehicles have a Cardan joint at each end and a telescoping device with sliding splines that adapts to changes in the distance between the connected mechanical members.
Although this solution is very widely used, it imposes severe technical limitations on vehicle designers as a result of these shortcomings of its components:
1) the velocity variations of the Cardan joints limit the maximum working angle to between 5 and 10.degree., depending on the rotative speed; PA1 2) the axial resistance to compression/elongation movements is high and essentially proportional to the transmitted torque, resulting in large axial reactions on the connected mechanical members. PA1 a) the ability to operate at a continuous angle at greater speed, for example at a speed about three times greater, and thus the ability to transmit triple the power at the same torque; PA1 b) the ability to adjust to a much larger angle: in contrast to the splined telescoping system, the insertion of which is independent of the angle of the Cardan joints and thus is theoretically unlimited, the insertion of a sliding constant-velocity joint is limited due to the obvious geometric reasons of conical deflection of the shaft inside the bowl. PA1 1. For ball-type joints: heat removal and wear, as well as insufficient angular adjustment, which limits their use to applications with a continuous working angle of about 4.degree.; PA1 2. For tripod joints: radial vibrations at high speed and insufficient angular adjustment; PA1 3. For solutions with a radially centered double Cardan joint with sliding splines: high cost and bulkiness, as well as the large axial reactions generated by the sliding splines; PA1 4. For solutions with four rollers: insufficient angular adjustment for a given outside diameter, for example, of the joint described in FR-A-2,566,858, which limits this solution to applications with little or no adjustment. PA1 an outer member or sleeve having on the inner peripheral wall four identical longitudinal races, each having two tracks parallel to the axis of said sleeve, the races being open inwardly and each having a radial symmetry plane at a right angle to the radial symmetry plane of the adjacent races; PA1 an inner input shaft carrying in the vicinity of its end a driving member that is attached to said shaft and that has on its periphery several equalizing levers, each designed to pivot in relation to the driver about a respective radial axis, said equalizing levers being evenly spaced on the periphery of said driver; PA1 two bipods mounted in a pivoting manner about the inner shaft on either side of the driver, each bipod having at each of its two opposite radial ends a respective roller having a peripheral bearing surface with a profile complementary to that of the corresponding race to allow it to roll in relation to said race, the axes of the four rollers being in the same plane perpendicular to the axis of the internal shaft; PA1 the equalizing levers being arranged so that the two bipods are always pivoted at the same angle in opposite directions in relation to the driver. PA1 the sleeve has on its inner peripheral wall four longitudinal recess grooves open inwardly, each groove being arranged along the diagonal between the two adjacent races; PA1 the driver has the form of a cross with four arms arranged radially at right angles to one another, the free end of each arm being shaped so that it can serve as the pivot for a corresponding equalizing lever; PA1 each bipod has four radial lugs arranged at right angles to one another and at 45.degree. to the axis of the rollers mounted on said bipod, and each lug has on the surface facing the driver a slot designed to receive an associated end of the corresponding equalizing lever; PA1 the recess grooves are dimensioned to let the bipod lugs and the equalizing levers pass without contact; PA1 means are provided to press the two bipods continually onto the ends of the equalizing levers, which are arranged so as to keep the inner surface of each bipod at a distance from the cross at all times in order to avoid any contact between either bipod and the cross.
To overcome these limitations, solutions have been proposed based on sliding constant-velocity joints, which have provided satisfactory power transmission in the transverse drives of front-wheel drive vehicles.
However, longitudinal drives require constant-velocity joints with higher performance, particularly:
The proposed solutions have shown their limitations, which can be summarized as follows:
Disclosed in U.S. Pat. No. 2,691,876 is a sliding constant-velocity joint comprising:
It follows from a study of this document that each equalizing lever has a central portion with a cylindrical outer contour seated in a peripheral slot, having a complementary inner cylindrical contour and a radial axis, arranged on the periphery of the driver, and that the inner surfaces of the two bipods contact the corresponding surfaces of the driver and pivot in relation to said corresponding surfaces.
What obtains then is a sliding constant-velocity joint consisting of two bipod joints that are inherently not of constant velocity and that are paired in such a manner that the departure from constant velocity of the first bipod is at every instant algebraically added to the departure from constant velocity of the second bipod. Because the axes of the rollers of the two bipods are on average perpendicular, the departures from constant velocity at every instant are of the same absolute value and in the opposite directions, and the sum of these is thus always zero.
However, in this joint, the maximum working angle and the maximum possible insertion for a given working angle are too small for most present applications, which require a double Cardan joint with a swivel and sliding splines.
In addition, the surfaces for torque transfer between the bipods and the shaft are much too small and are poorly situated inside the joint. Thus the lever arm is short and the lubrication is too precarious to ensure a sufficient capacity. Finally, the axial stacking of the principal parts causes complementary moments that result in excessive friction, mechanical losses, and wear that are incompatible with high-speed applications.